xref: /titanic_50/usr/src/uts/common/fs/smbsrv/smb_oplock.c (revision a90cf9f29973990687fa61de9f1f6ea22e924e40)

/*
 * CDDL HEADER START
 *
 * The contents of this file are subject to the terms of the
 * Common Development and Distribution License (the "License").
 * You may not use this file except in compliance with the License.
 *
 * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
 * or http://www.opensolaris.org/os/licensing.
 * See the License for the specific language governing permissions
 * and limitations under the License.
 *
 * When distributing Covered Code, include this CDDL HEADER in each
 * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
 * If applicable, add the following below this CDDL HEADER, with the
 * fields enclosed by brackets "[]" replaced with your own identifying
 * information: Portions Copyright [yyyy] [name of copyright owner]
 *
 * CDDL HEADER END
 */
/*
 * Copyright (c) 2007, 2010, Oracle and/or its affiliates. All rights reserved.
 * Copyright 2014 Nexenta Systems, Inc.  All rights reserved.
 */

/*
 * smb_oplock_wait / smb_oplock_broadcast
 * When an oplock is being acquired, we must ensure that the acquisition
 * response is submitted to the network stack before any other operation
 * is permitted on the oplock.
 * In smb_oplock_acquire, oplock.ol_xthread is set to point to the worker
 * thread processing the command that is granting the oplock.
 * Other threads accessing the oplock will be suspended in smb_oplock_wait().
 * They will be awakened when the worker thread referenced in 'ol_xthread'
 * calls smb_oplock_broadcast().
 *
 * The purpose of this mechanism is to prevent another thread from
 * triggering an oplock break before the response conveying the grant
 * has been sent.
 */

#include <smbsrv/smb_kproto.h>
#include <sys/nbmlock.h>

#define	SMB_OPLOCK_IS_EXCLUSIVE(level)		\
	(((level) == SMB_OPLOCK_EXCLUSIVE) ||	\
	((level) == SMB_OPLOCK_BATCH))

static int smb_oplock_install_fem(smb_node_t *);
static void smb_oplock_uninstall_fem(smb_node_t *);

static void smb_oplock_wait(smb_node_t *);
static void smb_oplock_wait_ack(smb_node_t *, uint32_t);
static void smb_oplock_timedout(smb_node_t *);

static smb_oplock_grant_t *smb_oplock_set_grant(smb_ofile_t *, uint8_t);
void smb_oplock_clear_grant(smb_oplock_grant_t *);
static int smb_oplock_insert_grant(smb_node_t *, smb_oplock_grant_t *);
static void smb_oplock_remove_grant(smb_node_t *, smb_oplock_grant_t *);
static smb_oplock_grant_t *smb_oplock_exclusive_grant(list_t *);
static smb_oplock_grant_t *smb_oplock_get_grant(smb_oplock_t *, smb_ofile_t *);

static void smb_oplock_sched_async_break(smb_oplock_grant_t *, uint8_t);
static void smb_oplock_exec_async_break(void *);
static void smb_oplock_break_levelII_locked(smb_node_t *);

/*
 * smb_oplock_install_fem
 * Install fem monitor for cross protocol oplock breaking.
 */
static int
smb_oplock_install_fem(smb_node_t *node)
{
	ASSERT(MUTEX_HELD(&node->n_oplock.ol_mutex));

	if (node->n_oplock.ol_fem == B_FALSE) {
		if (smb_fem_oplock_install(node) != 0) {
			cmn_err(CE_NOTE, "No oplock granted: "
			    "failed to install fem monitor %s",
			    node->vp->v_path);
			return (-1);
		}
		node->n_oplock.ol_fem = B_TRUE;
	}
	return (0);
}

/*
 * smb_oplock_uninstall_fem
 * Uninstall fem monitor for cross protocol oplock breaking.
 */
static void
smb_oplock_uninstall_fem(smb_node_t *node)
{
	ASSERT(MUTEX_HELD(&node->n_oplock.ol_mutex));

	if (node->n_oplock.ol_fem) {
		smb_fem_oplock_uninstall(node);
		node->n_oplock.ol_fem = B_FALSE;
	}
}

/*
 * This provides a way to fully disable oplocks, i.e. for testing.
 * You _really_ do _not_ want to turn this off, because if you do,
 * the clients send you very small read requests, and a _lot_ more
 * of them.  The skc_oplock_enable parameter can be used to enable
 * or disable exclusive oplocks.  Disabling that can be helpful
 * when there are clients not responding to oplock breaks.
 */
int smb_oplocks_enabled = 1;

/*
 * smb_oplock_acquire
 *
 * Attempt to acquire an oplock. Clients will request EXCLUSIVE or BATCH,
 * but might only be granted LEVEL_II or NONE.
 *
 * If oplocks are not supported on the tree, or node, grant NONE.
 * If nobody else has the file open, grant the requested level.
 * If any of the following are true, grant NONE:
 * - there is an exclusive oplock on the node
 * - op->op_oplock_levelII is B_FALSE (LEVEL_II not supported by open cmd.
 * - LEVEL_II oplocks are not supported for the session
 * - a BATCH oplock is requested on a named stream
 * - there are any range locks on the node (SMB writers)
 * Otherwise, grant LEVEL_II.
 *
 * ol->ol_xthread is set to the current thread to lock the oplock against
 * other operations until the acquire response is on the wire. When the
 * acquire response is on the wire, smb_oplock_broadcast() is called to
 * reset ol->ol_xthread and wake any waiting threads.
 */
void
smb_oplock_acquire(smb_request_t *sr, smb_node_t *node, smb_ofile_t *ofile)
{
	smb_oplock_t		*ol;
	smb_oplock_grant_t	*og;
	list_t			*grants;
	smb_arg_open_t		*op;
	smb_tree_t		*tree;
	smb_session_t		*session;

	SMB_NODE_VALID(node);
	SMB_OFILE_VALID(ofile);

	ASSERT(node == SMB_OFILE_GET_NODE(ofile));
	ASSERT(RW_LOCK_HELD(&node->n_lock));

	op = &sr->sr_open;
	tree = SMB_OFILE_GET_TREE(ofile);
	session = SMB_OFILE_GET_SESSION(ofile);

	if (smb_oplocks_enabled == 0 ||
	    (op->op_oplock_level == SMB_OPLOCK_NONE) ||
	    ((op->op_oplock_level == SMB_OPLOCK_BATCH) &&
	    SMB_IS_STREAM(node))) {
		op->op_oplock_level = SMB_OPLOCK_NONE;
		return;
	}

	ol = &node->n_oplock;
	grants = &ol->ol_grants;

	mutex_enter(&ol->ol_mutex);
	smb_oplock_wait(node);

	/*
	 * Even if there are no other opens, we might want to
	 * grant only a Level II (shared) oplock so we avoid
	 * ever granting exclusive oplocks.
	 *
	 * Borrowing the SMB_TREE_OPLOCKS flag to enable/disable
	 * exclusive oplocks (for now).  See skc_oplock_enable,
	 * which can now be taken as "exclusive oplock enable".
	 * Should rename this parameter, and/or implement a new
	 * multi-valued parameter for oplock enables.
	 */
	if ((node->n_open_count > 1) ||
	    (node->n_opening_count > 1) ||
	    !smb_tree_has_feature(tree, SMB_TREE_OPLOCKS) ||
	    smb_vop_other_opens(node->vp, ofile->f_mode)) {
		/*
		 * There are other opens.
		 */
		if ((!op->op_oplock_levelII) ||
		    (!smb_session_levelII_oplocks(session)) ||
		    (smb_oplock_exclusive_grant(grants) != NULL) ||
		    (smb_lock_range_access(sr, node, 0, 0, B_FALSE))) {
			/*
			 * LevelII (shared) oplock not allowed,
			 * so reply with "none".
			 */
			op->op_oplock_level = SMB_OPLOCK_NONE;
			mutex_exit(&ol->ol_mutex);
			return;
		}

		op->op_oplock_level = SMB_OPLOCK_LEVEL_II;
	}

	og = smb_oplock_set_grant(ofile, op->op_oplock_level);
	if (smb_oplock_insert_grant(node, og) != 0) {
		smb_oplock_clear_grant(og);
		op->op_oplock_level = SMB_OPLOCK_NONE;
		mutex_exit(&ol->ol_mutex);
		return;
	}

	ol->ol_xthread = curthread;
	mutex_exit(&ol->ol_mutex);
}

/*
 * smb_oplock_break
 *
 * Break granted oplocks according to the following rules:
 *
 * If there's an exclusive oplock granted on the node
 *  - if the BREAK_BATCH flags is specified and the oplock is not
 *    a batch oplock, no break is required.
 *  - if the session doesn't support LEVEL II oplocks, and 'brk' is
 *    BREAK_TO_LEVEL_II, do a BREAK_TO_NONE.
 *  - if the oplock is already breaking update the break level (if
 *    the requested break is to a lesser level), otherwise send an
 *    oplock break.
 *    Wait for acknowledgement of the break (unless NOWAIT flag is set)
 *
 * Otherwise:
 * If there are level II oplocks granted on the node, and the flags
 * indicate that they should be broken (BREAK_TO_NONE specified,
 * BREAK_EXCLUSIVE, BREAK_BATCH not specified) queue the levelII
 * break request for asynchronous processing.
 *
 * Returns:
 *       0 - oplock broken (or no break required)
 *  EAGAIN - oplock break request sent and would block
 *           awaiting the reponse but NOWAIT was specified
 *
 * NB: sr == NULL when called by FEM framework.
 */
int
smb_oplock_break(smb_request_t *sr, smb_node_t *node, uint32_t flags)
{
	smb_oplock_t		*ol;
	smb_oplock_grant_t	*og;
	list_t			*grants;
	uint32_t		timeout;
	uint8_t			brk;

	SMB_NODE_VALID(node);
	ol = &node->n_oplock;
	grants = &ol->ol_grants;

	mutex_enter(&ol->ol_mutex);
	smb_oplock_wait(node);

	og = list_head(grants);
	if (og == NULL) {
		mutex_exit(&ol->ol_mutex);
		return (0);
	}

	SMB_OPLOCK_GRANT_VALID(og);

	/* break levelII oplocks */
	if (og->og_level == SMB_OPLOCK_LEVEL_II) {
		mutex_exit(&ol->ol_mutex);

		if ((flags & SMB_OPLOCK_BREAK_TO_NONE) &&
		    !(flags & SMB_OPLOCK_BREAK_EXCLUSIVE) &&
		    !(flags & SMB_OPLOCK_BREAK_BATCH))  {
			smb_oplock_break_levelII(node);
		}
		return (0);
	}

	/* break exclusive oplock */
	if ((flags & SMB_OPLOCK_BREAK_BATCH) &&
	    (og->og_level != SMB_OPLOCK_BATCH)) {
		mutex_exit(&ol->ol_mutex);
		return (0);
	}

	if ((flags & SMB_OPLOCK_BREAK_TO_LEVEL_II) &&
	    smb_session_levelII_oplocks(og->og_session)) {
		brk = SMB_OPLOCK_BREAK_TO_LEVEL_II;
	} else {
		brk = SMB_OPLOCK_BREAK_TO_NONE;
	}

	switch (ol->ol_break) {
	case SMB_OPLOCK_NO_BREAK:
		ol->ol_break = brk;
		smb_oplock_sched_async_break(og, brk);
		break;
	case SMB_OPLOCK_BREAK_TO_LEVEL_II:
		if (brk == SMB_OPLOCK_BREAK_TO_NONE)
			ol->ol_break = SMB_OPLOCK_BREAK_TO_NONE;
		break;
	case SMB_OPLOCK_BREAK_TO_NONE:
	default:
		break;
	}

	if (flags & SMB_OPLOCK_BREAK_NOWAIT) {
		mutex_exit(&ol->ol_mutex);
		return (EAGAIN);
	}

	if (sr && (sr->session == og->og_session) &&
	    (sr->smb_uid == og->og_uid)) {
		timeout = smb_oplock_min_timeout;
	} else {
		timeout = smb_oplock_timeout;
	}

	mutex_exit(&ol->ol_mutex);
	smb_oplock_wait_ack(node, timeout);
	return (0);
}

/*
 * smb_oplock_break_levelII
 *
 * This is called after a file is modified in some way.  If there are
 * LevelII (shared) oplocks, break those to none.  If there is an
 * exclusive oplock, there can be no LevelII oplocks, so do nothing.
 *
 * LevelII (shared) oplock breaks are processed asynchronously.
 * Unlike exclusive oplock breaks, the thread initiating the break
 * is NOT blocked while the request is processed.
 *
 * There may be a thread with exclusive rights to oplock state for
 * this node (via ol_xthread in smb_oplock_wait) and if so, we must
 * avoid breaking oplocks until that's out of the way.  However, we
 * really don't want to block here, so when ol_xthread is set, we'll
 * just mark that a "break level II to none" is pending, and let the
 * exclusive thread do this work when it's done being exclusive.
 */
void
smb_oplock_break_levelII(smb_node_t *node)
{
	smb_oplock_t		*ol;

	ol = &node->n_oplock;
	mutex_enter(&ol->ol_mutex);

	/* Instead of: smb_oplock_wait() ... */
	if (ol->ol_xthread != NULL) {
		/* Defer the call to smb_oplock_broadcast(). */
		ol->ol_brk_pending = SMB_OPLOCK_BREAK_TO_NONE;
	} else {
		/* Equivalent of smb_oplock_wait() done. */
		smb_oplock_break_levelII_locked(node);
	}

	mutex_exit(&ol->ol_mutex);
}

/*
 * smb_oplock_break_levelII_locked
 * Internal helper for smb_oplock_break_levelII()
 *
 * Called with the oplock mutex already held, and _after_
 * (the equivalent of) an smb_oplock_wait().
 */
static void
smb_oplock_break_levelII_locked(smb_node_t *node)
{
	smb_oplock_t		*ol;
	smb_oplock_grant_t	*og;
	list_t			*grants;

	ol = &node->n_oplock;
	grants = &ol->ol_grants;

	ASSERT(MUTEX_HELD(&ol->ol_mutex));
	ASSERT(ol->ol_xthread == NULL);

	while ((og = list_head(grants)) != NULL) {
		SMB_OPLOCK_GRANT_VALID(og);

		/*
		 * If there's an exclusive oplock, there are
		 * no LevelII oplocks, so do nothing.
		 */
		if (SMB_OPLOCK_IS_EXCLUSIVE(og->og_level))
			break;

		smb_oplock_sched_async_break(og, SMB_OPLOCK_BREAK_TO_NONE);
		smb_oplock_remove_grant(node, og);
		smb_oplock_clear_grant(og);
	}
}

/*
 * Schedule a call to smb_session_oplock_break
 * using an smb_request on the owning session.
 */
static void
smb_oplock_sched_async_break(smb_oplock_grant_t *og, uint8_t brk)
{
	smb_request_t		*sr;
	smb_ofile_t		*ofile;

	/*
	 * Make sure we can get a hold on the ofile.  If we can't,
	 * the file is closing, and there's no point scheduling an
	 * oplock break on it.  (Also hold the tree and user.)
	 * These holds account for the pointers we copy into the
	 * smb_request fields: fid_ofile, tid_tree, uid_user.
	 * These holds are released via smb_request_free after
	 * the oplock break has been sent.
	 */
	ofile = og->og_ofile;
	if (!smb_ofile_hold(ofile))
		return;
	smb_tree_hold_internal(ofile->f_tree);
	smb_user_hold_internal(ofile->f_user);

	sr = smb_request_alloc(og->og_session, 0);
	sr->sr_state = SMB_REQ_STATE_SUBMITTED;
	sr->user_cr = zone_kcred();
	sr->fid_ofile = ofile;
	sr->tid_tree = ofile->f_tree;
	sr->uid_user = ofile->f_user;

	sr->arg.olbrk = *og; /* struct copy */
	sr->arg.olbrk.og_breaking = brk;

	(void) taskq_dispatch(
	    sr->sr_server->sv_worker_pool,
	    smb_oplock_exec_async_break, sr, TQ_SLEEP);
}

/*
 * smb_oplock_exec_async_break
 *
 * Called via the taskq to handle an asynchronous oplock break.
 * We have a hold on the ofile, which keeps the FID here valid.
 */
static void
smb_oplock_exec_async_break(void *arg)
{
	smb_request_t *sr = arg;
	smb_oplock_grant_t *og = &sr->arg.olbrk;

	SMB_REQ_VALID(sr);
	SMB_OPLOCK_GRANT_VALID(og);

	mutex_enter(&sr->sr_mutex);
	sr->sr_worker = curthread;
	sr->sr_time_active = gethrtime();

	switch (sr->sr_state) {
	case SMB_REQ_STATE_SUBMITTED:
		sr->sr_state = SMB_REQ_STATE_ACTIVE;
		mutex_exit(&sr->sr_mutex);

		/*
		 * This is where we actually do the deferred work
		 * requested by smb_oplock_sched_async_break().
		 */
		smb_session_oplock_break(sr, og->og_breaking);

		mutex_enter(&sr->sr_mutex);
		/* FALLTHROUGH */

	default: /* typically cancelled */
		sr->sr_state = SMB_REQ_STATE_COMPLETED;
		mutex_exit(&sr->sr_mutex);
	}

	smb_request_free(sr);
}

/*
 * smb_oplock_wait_ack
 *
 * Timed wait for an oplock break acknowledgement (or oplock release).
 */
static void
smb_oplock_wait_ack(smb_node_t *node, uint32_t timeout)
{
	smb_oplock_t	*ol;
	clock_t		time;

	ol = &node->n_oplock;
	mutex_enter(&ol->ol_mutex);
	time = MSEC_TO_TICK(timeout) + ddi_get_lbolt();

	while (ol->ol_break != SMB_OPLOCK_NO_BREAK) {
		if (cv_timedwait(&ol->ol_cv, &ol->ol_mutex, time) < 0) {
			smb_oplock_timedout(node);
			cv_broadcast(&ol->ol_cv);
			break;
		}
	}
	mutex_exit(&ol->ol_mutex);
}

/*
 * smb_oplock_timedout
 *
 * An oplock break has not been acknowledged within timeout
 * 'smb_oplock_timeout'.
 * Set oplock grant to the desired break level.
 */
static void
smb_oplock_timedout(smb_node_t *node)
{
	smb_oplock_t		*ol;
	smb_oplock_grant_t	*og;
	list_t			*grants;

	ol = &node->n_oplock;
	grants = &ol->ol_grants;

	ASSERT(MUTEX_HELD(&ol->ol_mutex));

	og = smb_oplock_exclusive_grant(grants);
	if (og) {
		switch (ol->ol_break) {
		case SMB_OPLOCK_BREAK_TO_NONE:
			og->og_level = SMB_OPLOCK_NONE;
			smb_oplock_remove_grant(node, og);
			smb_oplock_clear_grant(og);
			break;
		case SMB_OPLOCK_BREAK_TO_LEVEL_II:
			og->og_level = SMB_OPLOCK_LEVEL_II;
			break;
		default:
			SMB_PANIC();
		}
	}
	ol->ol_break = SMB_OPLOCK_NO_BREAK;
}

/*
 * smb_oplock_release
 *
 * Release the oplock granted on ofile 'of'.
 * Wake any threads waiting for an oplock break acknowledgement for
 * this oplock.
 * This is called when the ofile is being closed.
 */
void
smb_oplock_release(smb_node_t *node, smb_ofile_t *of)
{
	smb_oplock_t		*ol;
	smb_oplock_grant_t	*og;

	ol = &node->n_oplock;
	mutex_enter(&ol->ol_mutex);
	smb_oplock_wait(node);

	og = smb_oplock_get_grant(ol, of);
	if (og) {
		smb_oplock_remove_grant(node, og);
		smb_oplock_clear_grant(og);

		if (ol->ol_break != SMB_OPLOCK_NO_BREAK) {
			ol->ol_break = SMB_OPLOCK_NO_BREAK;
			cv_broadcast(&ol->ol_cv);
		}
	}

	mutex_exit(&ol->ol_mutex);
}

/*
 * smb_oplock_ack
 *
 * Process oplock acknowledgement received for ofile 'of'.
 * - oplock.ol_break is the break level that was requested.
 * - brk is the break level being acknowledged by the client.
 *
 * Update the oplock grant level to the lesser of ol_break and brk.
 * If the grant is now SMB_OPLOCK_NONE, remove the grant from the
 * oplock's grant list and delete it.
 * If the requested break level (ol_break) was NONE and the brk is
 * LEVEL_II, send another oplock break (NONE). Do not wait for an
 * acknowledgement.
 * Wake any threads waiting for the oplock break acknowledgement.
 */
void
smb_oplock_ack(smb_node_t *node, smb_ofile_t *of, uint8_t brk)
{
	smb_oplock_t		*ol;
	smb_oplock_grant_t	*og;

	ol = &node->n_oplock;
	mutex_enter(&ol->ol_mutex);
	smb_oplock_wait(node);

	if ((ol->ol_break == SMB_OPLOCK_NO_BREAK) ||
	    ((og = smb_oplock_get_grant(ol, of)) == NULL)) {
		mutex_exit(&ol->ol_mutex);
		return;
	}

	switch (brk) {
	case SMB_OPLOCK_BREAK_TO_NONE:
		og->og_level = SMB_OPLOCK_NONE;
		break;
	case SMB_OPLOCK_BREAK_TO_LEVEL_II:
		if (ol->ol_break == SMB_OPLOCK_BREAK_TO_LEVEL_II) {
			og->og_level = SMB_OPLOCK_LEVEL_II;
		} else {
			/* SMB_OPLOCK_BREAK_TO_NONE */
			og->og_level = SMB_OPLOCK_NONE;
			smb_oplock_sched_async_break(og,
			    SMB_OPLOCK_BREAK_TO_NONE);
		}
		break;
	default:
		SMB_PANIC();
	}

	if (og->og_level == SMB_OPLOCK_NONE) {
		smb_oplock_remove_grant(node, og);
		smb_oplock_clear_grant(og);
	}

	ol->ol_break = SMB_OPLOCK_NO_BREAK;
	cv_broadcast(&ol->ol_cv);

	mutex_exit(&ol->ol_mutex);
}

/*
 * smb_oplock_broadcast
 *
 * Called when an open with oplock request completes.
 *
 * ol->ol_xthread identifies the thread that was performing an oplock
 * acquire. Other threads may be blocked awaiting completion of the
 * acquire.
 * If the calling thread is ol_xthread, wake any waiting threads.
 */
void
smb_oplock_broadcast(smb_node_t *node)
{
	smb_oplock_t	*ol;

	SMB_NODE_VALID(node);
	ol = &node->n_oplock;

	mutex_enter(&ol->ol_mutex);
	if ((ol->ol_xthread != NULL) && (ol->ol_xthread == curthread)) {
		ol->ol_xthread = NULL;
		if (ol->ol_brk_pending) {
			ol->ol_brk_pending = 0;
			smb_oplock_break_levelII_locked(node);
		}
		cv_broadcast(&ol->ol_cv);
	}
	mutex_exit(&ol->ol_mutex);
}

/*
 * smb_oplock_wait
 *
 * Wait for the completion of an oplock acquire.
 * If ol_xthread is not NULL and doesn't contain the pointer to the
 * context of the calling thread, the caller will sleep until the
 * ol_xthread is reset to NULL (via smb_oplock_broadcast()).
 */
static void
smb_oplock_wait(smb_node_t *node)
{
	smb_oplock_t	*ol;

	ol = &node->n_oplock;
	ASSERT(MUTEX_HELD(&ol->ol_mutex));

	if ((ol->ol_xthread != NULL) && (ol->ol_xthread != curthread)) {
		while (ol->ol_xthread != NULL)
			cv_wait(&ol->ol_cv, &ol->ol_mutex);
	}
}

/*
 * smb_oplock_set_grant
 */
static smb_oplock_grant_t *
smb_oplock_set_grant(smb_ofile_t *of, uint8_t level)
{
	smb_oplock_grant_t	*og;

	og = &of->f_oplock_grant;

	og->og_magic = SMB_OPLOCK_GRANT_MAGIC;
	og->og_breaking = 0;
	og->og_level = level;
	og->og_ofile = of;
	og->og_fid = of->f_fid;
	og->og_tid = of->f_tree->t_tid;
	og->og_uid = of->f_user->u_uid;
	og->og_session = of->f_session;
	return (og);
}

/*
 * smb_oplock_clear_grant
 */
void
smb_oplock_clear_grant(smb_oplock_grant_t *og)
{
	bzero(og, sizeof (smb_oplock_grant_t));
}

/*
 * smb_oplock_insert_grant
 *
 * If there are no grants in the oplock's list install the fem
 * monitor.
 * Insert the grant into the list and increment the grant count.
 */
static int
smb_oplock_insert_grant(smb_node_t *node, smb_oplock_grant_t *og)
{
	smb_oplock_t *ol = &node->n_oplock;

	ASSERT(MUTEX_HELD(&ol->ol_mutex));

	if (ol->ol_count == 0) {
		if (smb_oplock_install_fem(node) != 0)
			return (-1);
	}

	list_insert_tail(&ol->ol_grants, og);
	++ol->ol_count;
	return (0);
}

/*
 * smb_oplock_remove_grant
 *
 * Remove the oplock grant from the list, decrement the grant count
 * and, if there are no other grants in the list, uninstall the fem
 * monitor.
 */
static void
smb_oplock_remove_grant(smb_node_t *node, smb_oplock_grant_t *og)
{
	smb_oplock_t *ol = &node->n_oplock;

	ASSERT(MUTEX_HELD(&ol->ol_mutex));
	ASSERT(ol->ol_count > 0);

	list_remove(&ol->ol_grants, og);
	if (--ol->ol_count == 0)
		smb_oplock_uninstall_fem(node);
}

/*
 * smb_oplock_exclusive_grant
 *
 * If an exclusive (EXCLUSIVE or BATCH) oplock grant exists,
 * return it. Otherwise return NULL.
 */
static smb_oplock_grant_t *
smb_oplock_exclusive_grant(list_t *grants)
{
	smb_oplock_grant_t	*og;

	og = list_head(grants);
	if (og) {
		SMB_OPLOCK_GRANT_VALID(og);
		if (SMB_OPLOCK_IS_EXCLUSIVE(og->og_level))
			return (og);
	}
	return (NULL);
}

/*
 * smb_oplock_get_grant
 *
 * Find oplock grant corresponding to the specified ofile.
 */
static smb_oplock_grant_t *
smb_oplock_get_grant(smb_oplock_t *ol, smb_ofile_t *ofile)
{
	ASSERT(MUTEX_HELD(&ol->ol_mutex));

	if (SMB_OFILE_OPLOCK_GRANTED(ofile))
		return (&ofile->f_oplock_grant);
	else
		return (NULL);
}